1. Field of the Invention
The present invention relates generally to pipeline leak detection methods and apparatus, and more particularly to an improved method and apparatus for quickly and accurately locating the source of a leak in a pipeline utilizing improved cross-correlation techniques which allow the entire length of pipe between two sensors to be scanned without requiring use of a fixed delay or reversal of sensor inputs.
2. Brief Description of the Prior Art
It has long been known that water or any other fluid escaping from a pressurized pipe produces a characteristic noise which is propagated along the pipe with a constant velocity in both directions away from the leak location. It is likewise known that by placing sensors on opposite sides of the leak, the leak noise will be received at different times depending upon the distance of each sensor from the leak. Since the propagating velocity can easily be determined the location of the leak can be determined as a function of the time difference. In the U.S. Pat. No. 4,083,229 to Alan Anway, a cross-correlation measurement technique is disclosed wherein one signal is progressively delayed relative to the other while the apparatus continues to compare the similarity between the two signals. This enables the device to measure the difference in travel time T.sub.d of the leak noise to the respective sensors. By determining the velocity of sound for the particular piperline under test and using the distance between the sensors, the apparatus can compute the leak position in accordance with the following formula: EQU L=[D-(V.times.T.sub.d)]/2
where L is the leak position, D is the overall distance between the sensors, V is the velocity of sound in the pipeline medium, and T.sub.d is the transit time difference.
One of the problems associated with such prior art correlation techniques is that, in order to scan the entire length of the pipe between the two sensors, a fixed delay must be introduced into one of the input data streams, or means must be provided for switching the device inputs. Not only does this add additional complexity to the apparatus, but it also means that a certain delay is introduced into the operational function before meaningful data can be accumulated.